TransfoParam_GR2M <- function(ParamIn, Direction) {
  
  NParam <- 2
  Bool <- is.matrix(ParamIn)
  
  if (Bool == FALSE) {
    ParamIn <- rbind(ParamIn)
  }
  if (ncol(ParamIn) != NParam) {
    stop(paste("the GR2M model requires ", NParam, " parameters \n", sep = ""))
    return(NULL)
  }
  
  if (Direction == "TR") {
    ParamOut      <-  ParamIn
    ParamOut[, 1] <- exp(ParamIn[, 1])
    ParamOut[, 2] <- ParamIn[, 2] / 4 + 2.5
  }
  if (Direction == "RT") {
    ParamOut      <-  ParamIn
    ParamOut[, 1] <- log(ParamIn[, 1])
    ParamOut[, 2] <- (ParamIn[, 2] - 2.5) * 4
  }
  
  if (Bool == FALSE) {
    ParamOut <- ParamOut[1, ]
  }
  return(ParamOut)
  
}